U.S. patent number 10,937,577 [Application Number 15/233,362] was granted by the patent office on 2021-03-02 for magnetic compound and production method thereof.
This patent grant is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The grantee listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Akira Kato, Kurima Kobayashi, Akira Manabe, Noritsugu Sakuma, Shunji Suzuki, Masao Yano.
United States Patent |
10,937,577 |
Sakuma , et al. |
March 2, 2021 |
Magnetic compound and production method thereof
Abstract
A magnetic compound represented by the formula
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d wherein R.sup.1 is one or more elements selected from the
group consisting of Sm, Pm, Er, Tm and Yb, R.sup.2 is one or more
elements selected from the group consisting of Zr, La, Ce, Pr, Nd,
Eu, Gd, Tb, Dy, Ho and Lu, T is one or more elements selected from
the group consisting of Ti, V, Mo, Si and W, M is one or more
elements selected from the group consisting of unavoidable impurity
elements, Al, Cr, Cu, Ga, Ag and Au, 0.ltoreq.x.ltoreq.0.7,
0.ltoreq.y.ltoreq.0.7, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c<7.7, and 0.ltoreq.d.ltoreq.3, the magnetic compound
having a ThMn.sub.12-type crystal structure, wherein the volume
fraction of .alpha.-(Fe, Co) phase is less than 12.3%.
Inventors: |
Sakuma; Noritsugu (Mishima,
JP), Yano; Masao (Sunto-gun, JP), Kato;
Akira (Mishima, JP), Manabe; Akira (Miyoshi,
JP), Suzuki; Shunji (Iwata, JP), Kobayashi;
Kurima (Fukuroi, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota |
N/A |
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI KAISHA
(Toyota, JP)
|
Family
ID: |
1000005395909 |
Appl.
No.: |
15/233,362 |
Filed: |
August 10, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20170084370 A1 |
Mar 23, 2017 |
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Foreign Application Priority Data
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Sep 17, 2015 [JP] |
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2015-184368 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F
1/0557 (20130101); H01F 1/055 (20130101); C22C
38/14 (20130101); H01F 1/0593 (20130101); C22C
38/10 (20130101); H01F 41/0293 (20130101); C22C
38/005 (20130101) |
Current International
Class: |
C22C
38/14 (20060101); H01F 1/055 (20060101); H01F
1/059 (20060101); H01F 41/02 (20060101); C22C
38/10 (20060101); C22C 38/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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104916382 |
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Sep 2015 |
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CN |
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H06-235051 |
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Aug 1994 |
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JP |
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H06-283316 |
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Oct 1994 |
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JP |
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H06-342706 |
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Dec 1994 |
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JP |
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2001-189206 |
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Jul 2001 |
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JP |
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2004-265907 |
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Sep 2004 |
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JP |
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2006-183151 |
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Jul 2006 |
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JP |
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2013-157487 |
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Aug 2013 |
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JP |
|
Other References
Yang, Ying-chang et al., "Magnetic and crystallographic properties
of novel Fe-rich rare-earth nitrides of the type RTiFe11N-?
(invited)", Journal of Applied Physics, Nov. 15, 1991, vol. 70, No.
10, pp. 6001-6005. cited by applicant .
Yang, Ying-chang et al., "Intrinsic magnetic properties of
SmTiFe10", Journal of Applied Physics, Apr. 15, 1988, vol. 63, No.
8, pp. 3702-3703. cited by applicant .
Satoshi Sugimoto et al. "Enhancement of Magnetic Properties of
Sm(Fe, Co, Ti)12 Melt-Spun Ribbons by Refining Crystallized
Grains". Materials Transactions, The Japan Institute of Metals,
vol. 32, No. 12, 1991, pp. 1180-1183. cited by applicant .
Hirayama et al., "NdFe12Nx Hard-Magnetic Compound with High
Magnetization and Anisotropy Field," Science Direct, Scripta
Materialia, 2015, vol. 95, pp. 70-72. cited by applicant .
Jan. 5, 2018 Office Action issued in U.S. Appl. No. 14/844,478.
cited by applicant .
Oct. 15, 2018 Office Action issued in U.S. Appl. No 14/844,478.
cited by applicant .
Thaddeus B. Massalski, "Binary Alloy Phase Diagrams", II Ed, Dec.
1990, pp. 1479-1480. cited by applicant .
Y. Wang et al., "Magnetic and Structural Studies in Sm-Fe--Ti
Magnets", Journal of Applied Physics, 1990, pp. 4954-4956, vol. 67,
No. 9. cited by applicant .
Mar. 6, 2019 Notice of Allowance issued in U.S. Appl. No.
15/380,079. cited by applicant.
|
Primary Examiner: Koshy; Jophy S.
Attorney, Agent or Firm: Oliff PLC
Claims
What is claimed is:
1. A magnetic compound, its composition being represented by the
formula in atomic percentage:
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d wherein R.sup.1 is Sm, R.sup.2 is Zr, T is Ti, M is one or
more unavoidable impurity elements, 0.ltoreq.x.ltoreq.0.7,
0.ltoreq.y.ltoreq.0.7, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c<7.7, and 0.ltoreq.d.ltoreq.2, and wherein the magnetic
compound has a ThMn.sub.12-type crystal structure and an
.alpha.-(Fe, Co) phase of less than 12.3% in volume fraction,
wherein when hexagons A, B and C are defined as: A: a six-membered
ring centering on a rare earth atom R.sup.1 and consisting of Fe
(8i) and Fe(8j) sites, B: a six-membered ring centering on an Fe
(8i)-Fe (8i) dumbbell and consisting of Fe (8i) and Fe(8j) sites,
and C: a six-membered ring centering on an Fe (8i)-rare earth atom
line and consisting of Fe(8j) and Fe(8f) sites, the
ThMn.sub.12--type crystal structure has these hexagons A, B and C
and the length in the axis a direction of hexagon A is 0.607 nm or
more and 0.612 nm or less.
2. The magnetic compound according to claim 1, wherein
0.ltoreq.x.ltoreq.0.4.
3. The magnetic compound according to claim 1, wherein
4.ltoreq.a.ltoreq.15.
4. The magnetic compound according to claim 1, wherein
3.8.ltoreq.c<7.7.
5. The magnetic compound according to claim 1, wherein
0.ltoreq.y.ltoreq.0.4.
6. The magnetic compound according to claim 1, wherein the volume
fraction of .alpha.-(Fe, Co) phase is 10% or less.
7. A method for producing the magnetic compound according to claim
1, comprising: a step of preparing a molten alloy, its composition
being represented by the formula in atomic percentage:
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d wherein R.sup.1 is Sm, R.sup.2 is Zr, T is Ti,
0.ltoreq.x.ltoreq.0.7, 0.ltoreq.y.ltoreq.0.7, 4.ltoreq.a.ltoreq.20
b=100-a-c-d, 0<c<7.7, and 0.ltoreq.d.ltoreq.2, and a step of
quenching the molten alloy at a rate of 1.times.10.sup.2 to
1.times.10.sup.7 K/sec.
8. The method according to claim 7, further comprising a step of
performing a heat treatment at 800 to 1,300.degree. C. for 2 to 120
hours after the quenching step.
9. The method according to claim 7, wherein
0.ltoreq.x.ltoreq.0.4.
10. The method according to claim 7, wherein
4.ltoreq.a.ltoreq.15.
11. The method according to claim 7, wherein
3.8.ltoreq.c<7.7.
12. The method according to claim 7, wherein 0.ltoreq.y.ltoreq.0.4.
Description
TECHNICAL FIELD
The present invention relates to a magnetic compound having a
ThMn.sub.12-type crystal structure and having high an anisotropic
magnetic field and high saturation magnetization, and a production
method thereof.
BACKGROUND ART
The application of a permanent magnet is expanding to a wide range
of fields including electronics, information and
telecommunications, medical cares, machine tools, and industrial
and automotive motors, and while an increasing demand for reduction
in the amount of carbon dioxide emission has encouraged spreading
of hybrid vehicle, energy saving in the industrial field,
enhancement of power generation efficiency, etc., expectations for
development of a high-characteristic permanent magnet are recently
further growing.
An Nd--Fe--B-based magnet currently dominating the market as a
high-performance magnet is also used as a magnet for a drive motor
of EV/PHV/HV. These days, more miniaturization and higher power
output (increase in the residual magnetization of a magnet) of a
motor are pursued, and in response thereto, a new permanent magnet
material is being developed.
As one material having performance surpassing that of an Nd--Fe--B
magnet, a rare earth-iron-based magnetic compound having a
ThMn.sub.12-type crystal structure is currently being studied. For
example, a nitride magnetic composition containing Nd as a rare
earth element and having a ThMn.sub.12-type crystal structure has
been proposed in J. Appl. Phys., 70(10), 6001 (1991), and a
magnetic composition containing Sm as a rare earth element and
having a ThMn.sub.12-type crystal structure has been proposed in J.
Appl. Phys., 63(8), 3702 (1988).
SUMMARY OF THE INVENTION
In the conventionally known compounds having a NdFe.sub.11TiN.sub.x
composition containing a ThMn.sub.12-type crystal structure,
uniaxial magnetic anisotropy is developed by N and therefore, the
anisotropic magnetic field is high. However, since N desorbs at a
high temperature of 600.degree. C. or more to decrease the
anisotropic magnetic field, it has been difficult to achieve a high
performance by full densification such as sintering. On the other
hand, an SmFe.sub.11Ti compound containing Sm above is
substantially free of N and is advantageous in view of full
densification. However, sufficiently high magnetic properties have
not been heretofore obtained by the SmFe.sub.11Ti compound.
An object of the present invention is to provide a magnetic
compound having both high anisotropic magnetic field and high
magnetization, which can solve the problems in the related arts
above.
In order to attain the object above, according to the present
invention, the followings are provided.
(1) A magnetic compound represented by the formula:
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d wherein R.sup.1 is one or more elements selected from the
group consisting of Sm, Pm, Er, Tm and Yb,
R.sup.2 is one or more elements selected from the group consisting
of Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho and Lu,
T is one or more elements selected from the group consisting of Ti,
V, Mo, Si and W,
M is one or more elements selected from the group consisting of
unavoidable impurity elements, Al, Cr, Cu, Ga, Ag and Au,
0.ltoreq.x.ltoreq.0.7,
0.ltoreq.y.ltoreq.0.7,
4.ltoreq.a.ltoreq.20,
b=100-a-c-d,
0<c<7.7, and
0.ltoreq.d.ltoreq.3,
the magnetic compound having a ThMn.sub.12-type crystal structure,
wherein the volume fraction of .alpha.-(Fe, Co) phase is less than
12.3%.
(2) The magnetic compound according to (1), wherein when hexagons
A, B and C are defined as:
A: a six-membered ring centering on a rare earth atom R.sup.1 and
consisting of Fe (8i) and Fe(8j) sites,
B: a six-membered ring centering on an Fe (8i)-Fe (8i) dumbbell and
consisting of Fe (8i) and Fe(8j) sites, and
C: a six-membered ring centering on an Fe (8i)- rare earth atom
line and consisting of Fe (8j) and Fe(8f) sites,
the ThMn.sub.12-type crystal structure has these hexagons A, B and
C and the length in the axis a direction of hexagon A is 0.612 nm
or less.
(3) A method for producing the magnetic compound according to (1),
including:
a step of preparing a molten alloy having a composition represented
by the formula:
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d wherein R.sup.1 is one or more elements selected from the
group consisting of Sm, Pm, Er, Tm and Yb,
R.sup.2 is one or more elements selected from the group consisting
of Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho and Lu,
T is one or more elements selected from the group consisting of Ti,
V, Mo, Si and W,
M is one or more elements selected from the group consisting of
unavoidable impurity elements, Al, Cr, Cu, Ga, Ag and Au,
0.ltoreq.x.ltoreq.0.7,
0.ltoreq.y.ltoreq.0.7,
4.ltoreq.a.ltoreq.20,
b=100-a-c-d,
0<c<7.7, and
0.ltoreq.d.ltoreq.3,
and
a step of quenching the molten alloy at a rate of 1.times.10.sup.2
to 1.times.10.sup.7 K/sec.
The method according to (3), further including a step of performing
a heat treatment at 800 to 1,300.degree. C. for 2 to 120 hours
after the quenching step.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph illustrating various rare earth elements and the
values of the Stevens factor thereof.
FIG. 2 is a perspective view schematically illustrating the
ThMn.sub.12-type crystal structure.
FIGS. 3(a) and 3(b) are perspective views schematically
illustrating hexagons A, B and C in the ThMn.sub.12-type crystal
structure.
FIG. 4 is a view schematically illustrating the change in size of
the hexagon.
FIG. 5 is a schematic view of the apparatus used in a strip casting
method.
FIG. 6 is a graph illustrating the results from measuring the
saturation magnetization (room temperature) and the anisotropic
magnetic field in Examples 1 to 3 and Comparative Examples 1 to
10.
FIG. 7 is a graph illustrating the results from measuring the
saturation magnetization (180.degree. C.) and the anisotropic
magnetic field in Examples 1 to 3 and Comparative Examples 1 to
10.
FIG. 8 is a graph illustrating the results from measuring the
saturation magnetization (room temperature) and the anisotropic
magnetic field in Examples 4 and 5 and Comparative Examples 11 and
12.
FIG. 9 is a graph illustrating the results from measuring the
saturation magnetization (180.degree. C.) and the anisotropic
magnetic field in Examples 4 and 5 and Comparative Examples 11 and
12.
FIG. 10 is a graph illustrating the relationship between the amount
of R.sup.2 and the magnetic properties (anisotropic magnetic field)
in Examples and Comparative Examples.
FIG. 11 is a graph illustrating the relationship between the amount
of R.sup.2 and the magnetic properties (anisotropic magnetic field)
in Examples and Comparative Examples.
MODE FOR CARRYING OUT THE INVENTION
The magnetic compound according to the present invention is
described in detail below. The magnetic compound of the present
invention is a magnetic compound represented by the following
formula:
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d and each constituent component is described below.
(R.sup.1)
R.sup.1 is a rare earth element having a positive Stevens factor
and is an essential component in the magnetic compound of the
present invention so as to develop permanent magnet
characteristics. In FIG. 1, various rare earth elements and the
values of the Stevens factor thereof are illustrated. Specifically,
R.sup.1 is one or more elements selected from the group consisting
of Sm, Pm, Er, Tm and Yb each having a positive Stevens factor
illustrated in FIG. 1, and it is particularly preferable to use Sm
having a high value of the Stevens factor.
The Stevens factor is a parameter depending on the spatial
distribution geometry of 4f electrons and takes a fixed value
according to the kind of the rare earth ion R.sup.3+. The 4f
electron shows a characteristic spatial distribution according to
the number of the electrons and in the case of Gd.sup.3+ ion having
seven 4f electrons, seven 4f orbitals are filled with 4f electrons
having seven upward spins and since the orbital magnetic moments
cancel one another and become 0, the existence probability of 4f
electrons produces a spherical distribution. On the other hand, for
example, in the case of Nd.sup.3+ or Dy, since the Stevens factor
is negative, the spatial distribution of 4f electrons is distorted
relative to axis z that is a symmetry axis, and the existence
probability of 4f electrons has a flat profile. On the contrary,
for example, in the case of Sm.sup.3+, since the Stevens factor is
positive, the spatial distribution of 4f electrons extends relative
to axis z that is a symmetry axis, and the existence probability of
4f electrons has an oblong profile.
In the case of using a rare earth element having a negative Stevens
factor, spin is not fixed due to a flat profile of the existence
probability of 4f electrons, and nitridation needs to be performed
so as to produce uniaxial anisotropy, but a sintering step cannot
be used at the time of manufacture of a full-dense magnet (because
sintering performed at a high temperature causes nitrogen leakage
at the high temperature during sintering or makes the ThMn.sub.12
structure unstable at the high temperature, resulting in
decomposition into a rare earth nitride and .alpha.-Fe), and the
usage remains at the level of bonded magnet. On the other hand, in
the case of using a rare earth magnet having a positive Stevens
factor, it is known that uniaxial anisotropy is developed, and
nitridation need not be performed.
(R.sup.2)
R.sup.2 is Zr or one or more elements selected from the group
consisting of La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho and Lu in which
the Stevens factor is negative or zero, and contributes to
stabilization of the ThMn.sub.12-type crystal phase by substituting
for part of the rare earth element R.sup.1. More specifically,
R.sup.2, particularly, Zr element, substitutes for R.sup.1 element
in the ThMn.sub.12-type crystal to cause shrinkage of a crystal
lattice and thereby acts to stably maintain the ThMn.sub.12-type
crystal phase when the temperature of an alloy is raised or a
nitrogen atom, etc. is entered into a crystal lattice. In addition,
one or more elements selected from the group consisting of La, Ce,
Pr, Nd, Eu, Gd, Tb, Dy, Ho and Lu in which the Stevens factor is
negative or zero, bear little resource risk compared with Sm and
consequently, by replacing part of the rare earth site by La, etc.,
a magnet more reduced in the resource risk can be manufactured. On
the other hand, from the standpoint of magnetic properties, since
the strong magnetic anisotropy derived from R.sup.1 element is
weakened by R.sup.2 substitution, the R.sup.2 amount must be
determined by taking into account the stability of crystal and the
magnetic properties. However, in the present invention, addition of
R.sup.2 is not essential. The R.sup.2 amount x is
0.ltoreq.x.ltoreq.0.7, and when the R.sup.2 amount is 0, the
ThMn.sub.12-type crystal phase can be stabilized, for example, by
adjusting the component composition of alloy and performing a heat
treatment, which in turn increases the anisotropic magnetic field.
If the R.sup.2 substitution amount exceeds 0.7, the anisotropic
magnetic field significantly decreases. The R.sup.2 amount x is
preferably 0.ltoreq.x.ltoreq.0.4.
The total blending amount a of R.sup.1 and R.sup.2 is set to be
from 4 to 20 atom %, because if the blending amount is less than 4
atom %, precipitation of Fe phase becomes significant, and the
volume fraction of Fe phase cannot be decreased after heat
treatment, whereas if the blending amount is more than 20 atom %,
magnetization is not improved due to an excessively large amount of
grain boundary phase. The total blending amount a of R.sup.1 and
R.sup.2 is preferably 4.ltoreq.a.ltoreq.15.
(T)
T is one or more elements selected from the group consisting of Ti,
V, Mo, Si and W. It is known that when Ti, V, Mo, Si or W is added
as a third element to an R--Fe binary alloy (R: a rare earth
element), the ThMn.sub.12-type crystal structure is stabilized and
excellent magnetic properties are exhibited.
Conventionally, the ThMn.sub.12-type crystal structure is formed by
adding a T component in a large amount more than necessary to an
alloy so as to obtain the stabilization effect of this component
and therefore, the content by percentage of the Fe component
constituting the compound in the alloy is decreased. At the same
time, the site occupied by Fe atom having a largest effect on
magnetization is replaced, for example, by Ti atom, leading to
reduction in the entire magnetization. The magnetization may be
enhanced by decreasing the blending amount of Ti, but in this case,
stabilization of the ThMn.sub.12-type crystal structure is
deteriorated. As the conventional RFe.sub.12-xTi.sub.x compound,
RFe.sub.11Ti has been reported, but a compound in which x is less
than 1, i.e., Ti is less than 7.7 atom %, has not been
reported.
When the amount of Ti acting to stabilize the ThMn.sub.2-type
crystal structure is decreased, stabilization of the
ThMn.sub.12-type crystal structure is deteriorated, and
.alpha.-(Fe, Co) working out to a hindrance to the anisotropic
magnetic field or coercive force precipitates. In the present
invention, it is made possible to reduce the amount of .alpha.-(Fe,
Co) precipitated by controlling the cooling rate of molten alloy
and even when the blending amount of the T component is decreased,
stably produce a ThMn.sub.12 phase having high magnetic properties
by adjusting the volume fraction of .alpha.-(Fe, Co) phase in the
compound to a certain value or less.
The blending amount of the T component is an amount satisfying x of
less than 1 in the RFe.sub.12-xTi.sub.x compound, i.e., less than
7.7 atom %. If the blending amount is 7.7 atom % or more, the
content by percentage of the Fe component constituting the compound
is decreased, and the entire magnetization is reduced. The blending
amount c of the T component is preferably
3.8.ltoreq.c.ltoreq.7.7.
(M)
M is one or more elements selected from the group consisting of
unavoidable impurity elements, Al, Cr, Cu, Ga, Ag and Au. The
unavoidable impurity element means an element entering into the raw
material or an element getting mixed with in the production process
and, specifically, includes B, C, N, O, H, P and Mn. M contributes
to suppressing the grain growth of ThMn.sub.12-type crystal as well
as to the viscosity and melting point of a phase other than the
ThMn.sub.12-type crystal (for example, a grain boundary phase) but
is not essential in the present invention. The blending amount d of
M is 3 atom % or less, preferably 2 atom % or less. If the blending
amount is more than 3 atom %, the content by percentage of the Fe
component constituting the compound in the alloy is decreased, and
the entire magnetization is reduced.
(Fe and Co)
In the compound of the present invention, the remainder other than
the above-described elements is Fe, and part of Fe may be
substituted by Co. By substituting for Fe, Co can cause an increase
in the spontaneous magnetization according to the Slater-Pauling
Rule and enhance both properties of anisotropic magnetic field and
saturation magnetization. However, if the Co substitution amount
exceeds 0.7, the effects cannot be brought out. When Fe is
substituted by Co, the Curie point of the compound rises, and this
produces an effect of suppressing reduction in the magnetization at
a high temperature. The Co substitution amount y is preferably
0.ltoreq.y.ltoreq.0.4.
The magnetic compound of the present invention is characterized by
being represented by the formula above and having a
ThMn.sub.12-type crystal structure. This ThMn.sub.12-type crystal
structure is tetragonal and shows peaks at 2.theta. values of
29.801.degree., 36.554.degree., 42.082.degree., 42.368.degree., and
43.219.degree. (.+-.0.5.degree.) in the XRD measurement results.
Furthermore, the magnetic compound of the present invention is
characterized in that the volume fraction of .alpha.-(Fe, Co) phase
is less than 12.3%, preferably 10% or less, more preferably 8.4% or
less. This volume fraction is calculated from the area percentage
of the .alpha.-(Fe, Co) phase in a cross-section by image analysis
after a sample is embedded in a resin, polished and observed by OM
or SEM-EDX. Here, when it is assumed that the structure is not
randomly oriented, the following relational expression is
established between the average area percentage A and the volume
percentage V.
A=about V
In the present invention, the thus-measured area percentage of the
.alpha.-(Fe, Co) phase is taken as the volume fraction.
As described above, in the magnetic compound of the present
invention, the anisotropic magnetic field can be increased by
using, as a rare earth element, an element having a positive
Stevens factor and magnetization can be enhanced by decreasing the
content of the T component as compared to the conventional
RFe.sub.11Ti-type compound. In addition, the anisotropic magnetic
field can be improved by setting the volume fraction of the
.alpha.-(Fe, Co) phase to be as small as less than 12.3%.
(Crystal Structure)
The magnetic compound of the present invention is a rare earth
element-containing magnetic compound having a ThMn.sub.12-type
tetragonal crystal structure illustrated in FIG. 2. This is a
magnetic compound where as illustrated in FIG. 3, when hexagons A,
B and C are defined as:
A: a six-membered ring centering on a rare earth atom R.sup.1 and
consisting of Fe (8i) and Fe(8j) sites (FIG. 3(a)),
B: a six-membered ring centering on an Fe (8i)-Fe (8i) dumbbell and
consisting of Fe (8i) and Fe(8j) sites (FIG. 3(a)), and
C: a six-membered ring centering on an Fe (8i)- rare earth atom
line and consisting of Fe (8j) and Fe(8f) sites (FIG. 3(b)),
the length in the axis a direction of hexagon A: Hex(A) is 0.612 nm
or less.
As illustrated in FIG. 4, in the magnetic compound of the present
invention where the proportion of T (for example, Ti) as a
stabilization element is small and Ti having a large atomic radius
is replaced by Fe, compared with the conventional magnetic
compound, the shape or dimension balance of hexagon A is
deteriorated, but the deterioration is compensated for with Zr,
etc. having a smaller atomic radius than Sm, and the shape or
dimension balance is thereby adjusted.
(Production Method)
The magnetic compound of the present invention can be basically
produced by a conventional production method such as die casting
method or arc melting method, but in the conventional method, a
large amount of a stable phase (.alpha.-(Fe, Co) phase) except for
the ThMn.sub.12 phase is precipitated to decrease the anisotropic
magnetic field. In the present invention, focusing attention on the
relationship of temperature at which the ThMn.sub.12-type crystal
precipitates<temperature at which .alpha.-(Fe, Co) precipitates,
the molten alloy is quenched at a rate of 1.times.10.sup.2 to
1.times.10.sup.7 K/sec and thereby prevented from staying long near
the temperature at which .alpha.-(Fe, Co) precipitates, so as to
reduce the precipitation of .alpha.-(Fe, Co) and produce a large
amount of the ThMn.sub.12-type crystal.
As for the cooling method, for example, the molten alloy can be
cooled at a predetermined rate, for example, by a strip casting
method or a super-quenching method, by using an apparatus 10
illustrated in FIG. 5. In the apparatus 10, alloy raw materials are
melted in a melting furnace 11 to prepare a molten alloy 12 having
a composition represented by the formula
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.-
bT.sub.cM.sub.d. In the formula above, R.sup.1 is one or more
elements selected from the group consisting of Sm, Pm, Er, Tm and
Yb, R.sup.2 is one or more elements selected from the group
consisting of Zr, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho and Lu, T is
one or more elements selected from the group consisting of Ti, V,
Mo and W, M is one or more elements selected from the group
consisting of unavoidable impurity elements, Al, Cr, Cu, Ga, Ag and
Au, 0.ltoreq.x.ltoreq.0.7, 0.ltoreq.y.ltoreq.0.7,
4.ltoreq.a.ltoreq.20, b=100-a-c-d, 0<c<7.7, and
0.ltoreq.d.ltoreq.3. This molten alloy 12 is supplied to a tundish
13 at a fixed supply rate. The molten alloy 12 supplied to the
tundish 13 is continuously supplied to a cooling roller 14 through
a tapping hole at the end or bottom of the tundish 13.
The tundish 13 is composed of alumina, zirconia or ceramic such as
calcia and can temporarily store the molten alloy 12 continuously
supplied from the melting furnace 11 at a predetermined flow rate
and rectify the flow of the molten alloy 12 to the cooling roller
14. The tundish 13 also has a function of adjusting the temperature
of the molten alloy 12 immediately before reaching the cooling
roller 14.
The cooling roller 14 is formed of a material having high thermal
conductivity, such as copper or chromium alloy, and the roller
surface is subjected to chromium plating, etc. so as to prevent
corrosion from the high-temperature molten alloy. This roller is
rotated by a driving device (not shown) at a predetermined
rotational speed in the arrow direction. The cooling rate of the
molten alloy can be controlled to a rate of 1.times.10.sup.2 to
1.times.10.sup.7 K/sec by controlling the rotational speed.
The molten alloy 12 cooled and solidified on the outer
circumference of the cooling roller 14 turns into a flaky
solidified alloy 15 and is separated from the cooling roller 14,
crushed and collected in a collection device.
In the present invention, the method may further includes a step of
heat-treating the particle obtained in the step above at 800 to
1,300.degree. C. for 2 to 120 hours. By this heat treatment, the
ThMn.sub.12 phase is homogenized, and both properties of
anisotropic magnetic field and saturation magnetization are further
enhanced.
EXAMPLES
Examples 1 to 3 and Comparative Examples 1 to 9
Molten alloys aimed for the manufacture of a compound having the
composition shown in Table 1 below were prepared, and each was
quenched at a rate of 10.sup.4 K/sec by a strip casting method to
prepare a quenched flake. The flake was subjected to a heat
treatment in an Ar atmosphere at 1,200.degree. C. for 4 hours and
then crushed by means of a cutter mill in an Ar atmosphere, and
particles having a particle diameter of 30 .mu.m or less were
collected. The size and area percentage of .alpha.-(Fe, Co) phase
were measured from an SEM image (reflection electron image) of the
obtained particle, and the volume percentage was calculated
assuming that area percentage=volume percentage. In addition,
magnetic characteristic evaluation (VSM) and crystal structure
analysis (XRD) of the obtained particle were performed. The results
are shown in Table 1 and FIGS. 6 and 7.
TABLE-US-00001 TABLE 1 Ti Anisotropic Amount Size of Volume
Magnetic Saturation Saturation Hex. [atom .alpha.(Fe, Co)
Percentage of Field Magnetization Magnetization (A) Composition %]
(.mu.m) .alpha.(Fe, Co) (%) [MA/m] @RT (T) @180.degree. C. (T) (nm)
Example 1 Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.5Ti.sub.3.8 3.8
1.3 5.- 5 6.1 1.61 1.60 0.612 Example 2
(Sm.sub.0.8Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.5T-
i.sub.5.8 5.8 <1 <3.5 6.4 1.51 1.50 0.607 Example 3
(Sm.sub.0.8Ce.sub.0.1Zr.sub.0.1).sub.7.7(Fe.sub.0.75Co.sub.0.25)-
.sub.86.5Ti.sub.5.8 5.8 <1 <3.5 5.9 1.5 1.49 0.611
Comparative
(Nd.sub.0.7Zr.sub.0.3).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.-
5Ti.sub.3.8 3.8 1.1 3.9 1.3 1.65 1.62 0.603 Example 1 Comparative
Ce.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.5Ti.sub.5.8 5.8 <- 1
<3.5 1.9 1.3 1.38 0.619 Example 2 Comparative
(Ce.sub.0.8Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.-
5Ti.sub.5.8 5.8 <1 <3.5 1.7 1.42 1.40 0.610 Example 3
Comparative
(Nd.sub.0.9Zr.sub.0.1).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.-
5Ti.sub.5.8 5.8 <1 <3.5 1.7 1.59 1.56 0.615 Example 4
Comparative
(Nd.sub.0.8Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.-
5Ti.sub.5.8 5.8 <1 <3.5 1.7 1.6 1.57 0.610 Example 5
Comparative
(Nd.sub.0.7Zr.sub.0.3).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.-
5Ti.sub.5.8 5.8 <1 <3.5 1.7 1.57 1.54 0.606 Example 6
Comparative Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.84.6Ti.sub.7.7
7.7 <- 1 <3.5 6.7 1.32 1.30 0.618 Example 7 Comparative
Sm.sub.7.7Fe.sub.84.6Ti.sub.7.7 7.7 <1 <3.5 6.6 1.22 1.1- 2
0.618 Example 8 Comparative Sm.sub.7.7Fe.sub.80.8Ti.sub.11.5 11.5
<1 <3.5 6.8 1.19 1- .09 0.623 Example 9
As apparent from the results shown in Table 1 and FIGS. 6 and 7,
when the Ti amount is less than 7.7 atom %, a high value of
saturation magnetization is exhibited at room temperature and
180.degree. C. In particular, the value of saturation magnetization
at 180.degree. C. is significantly higher than the saturation
magnetization (1.3 T) of NdFeB at 180.degree. C. On the other hand,
in Samples 1 to 6 of Comparative Example where a rare earth element
having a negative Stevens factor, such as Nd or Ce, is used instead
of Sm, a large anisotropic magnetic field is not obtained. In
Samples 7 and 8 of Comparative Example where the Ti content by
percentage is as large as 7.7, the saturation magnetization is
low.
Here, in the crystal structure, when hexagons A, B and C are
defined as:
A: a six-membered ring centering on a rare earth atom R.sup.1 and
consisting of Fe (8i) and Fe(8j) sites,
B: a six-membered ring centering on an Fe (8i)-Fe (8i) dumbbell and
consisting of Fe (8i) and Fe(8j) sites, and
C: a six-membered ring centering on an Fe (8i)- rare earth atom
line and consisting of Fe (8j) and Fe(8f) sites,
the length Hex(A) in the axis a direction of hexagon A is estimated
from Table 1 to be 0.618 nm in the conventional magnetic compound
(Comparative Example 8), but it is understood that when Ti is
substituted by Fe and Sm is substituted by Zr, the value above
decreases. The reason therefor is considered to be that when the Ti
amount is decreased, a Ti atom of the 8i site of hexagon A is
replaced by an Fe atom having a small atomic radius to deteriorate
the size balance of hexagon A and disturb stable formation of a
1-12 phase but since the size balance was compensated for by
substituting for the Sm atom by Zr having a smaller atomic radius,
a 1-12 phase could be produced, despite decrease in the Ti
amount.
Examples 4 and 5
Molten alloys aimed for the manufacture of a compound having the
composition shown in Table 2 below were prepared, and each was
quenched at a rate of 10.sup.4 K/sec by a strip casting method to
prepare a quenched flake. In Example 5, the flake was then
subjected to a heat treatment in an Ar atmosphere at 1,200.degree.
C. for 4 hours. Subsequently, the flake was crushed by means of a
cutter mill in an Ar atmosphere, and particles having a particle
diameter of 30 .mu.m or less were collected. In the same manner as
in Example 1, the obtained particle was measured for the size and
area percentage of .alpha.-(Fe, Co) phase, and the volume
percentage was calculated. In addition, magnetic characteristic
evaluation (VSM) and crystal structure analysis (XRD) of the
obtained particle were performed. The results are shown in Table 2
and FIGS. 8 and 9.
Comparative Examples 10 and 11
Each of alloys aimed for the manufacture of a compound having the
composition shown in Table 2 below was arc-melted and cooled at a
rate of 50 K/sec to prepare a flake. In Comparative Example 11, the
flake was then subjected to a heat treatment in an Ar atmosphere at
1,200.degree. C. for 4 hours. Subsequently, the flake was crushed
by means of a cutter mill in an Ar atmosphere, and particles having
a particle diameter of 30 .mu.m or less were collected. The
obtained particle was nitrided at 450.degree. C. for 4 hours in a
nitrogen gas with purity of 99.99%. Magnetic characteristic
evaluation (VSM) and crystal structure analysis (XRD) of the
obtained particle were performed, and the results are shown in
Table 2 and FIGS. 8 and 9 together with the results from measuring
the size and area fraction of .alpha.-(Fe, Co) phase in the same
manner as in Example 1.
TABLE-US-00002 TABLE 2 Homoge- Volume Anisotropic Melting nization
Size of Percentage Magnetic Saturation Saturation Hex. Method, Heat
.alpha.(Fe, Co) of .alpha.(Fe, Co) Field Magnetization
Magnetization (A) Composition Cooling Rate Treatment (.mu.m) (%)
(MA/m) @RT (T) @180.degree. C. (T) (nm) Comparative
Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.5Ti.sub.3.8 arc melting
none 8 18.2 3.2 1.64 1.63 0.612 Example 10 50 K/s Comparative
Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.5Ti.sub.3.8 arc melting
1200.degree. C., 5 12.3 3.4 1.63 1.62 0.612 Example 11 50 K/s 4
hours Example 4
Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.5Ti.sub.38 quenching n-
one 1.5 8.4 5.5 1.62 1.61 0.612 10.sup.4 K/s Example 5
Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.5Ti.sub.38 quenching 1-
200.degree. C. 1.3 5.5 6.1 1.61 1.60 0.612 10.sup.4 K/s 4 hours
As seen from the results above, the size of .alpha.-(Fe, Co) phase
and the volume percentage thereof are decreased in the order of
Comparative Example 10 (arc melting).fwdarw.Comparative Example 11
(arc melting+homogenization heat treatment).fwdarw.Example 4
(quenching).fwdarw.Example 5 (quenching+homogenization heat
treatment). It is considered that quenching allows the .alpha.-(Fe,
Co) phase to become fine and be decreased in the precipitation
amount and furthermore, allows the entire structure to become fine
and undergo homogeneous dispersion and the properties are thereby
enhanced. In addition, it is considered that by further performing
a heat treatment after cooling, homogenization of the fine
structure proceeds and the proportion of .alpha.(Fe, Co) phase is
reduced, as a result, the anisotropic magnetic field is more
enhanced. In this way, even when the Ti amount is decreased,
precipitation of the .alpha.-(Fe, Co) phase is suppressed by
quenching treatment and homogenization heat treatment, and an
anisotropic magnetic field (about 6 MA/m) equivalent to that of
conventional SmFe.sub.11Ti or NdFeB is developed, which makes it
possible to manufacture a magnetic compound having a
ThMn.sub.12-type crystal structure and satisfying both properties
of anisotropic magnetic field and saturation magnetization at high
levels.
Examples 6 to 9 and Comparative Examples 12 to 19
Molten alloys aimed for the manufacture of a compound having the
composition shown in Table 3 below were prepared, and each was
quenched at a rate of 10.sup.4 K/sec by a strip casting method to
prepare a quenched flake. The flake was subjected to a heat
treatment in an Ar atmosphere at 1,200.degree. C. for 4 hours and
then crushed by means of a cutter mill in an Ar atmosphere, and
particles having a particle diameter of 30 .mu.m or less were
collected. Magnetic characteristic evaluation (VSM) and crystal
structure analysis (XRD) of the obtained particle were performed.
The results are shown in Table 3 and FIGS. 10 and 11.
TABLE-US-00003 TABLE 3 Anisotropic Saturation Saturation Hex. Ratio
Magnetic Magnetization Magnetization (A) Composition of R.sup.2
Field [MA/m] @RT (T) @180.degree. C. (T) (nm) Example 1
Sm.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.88.5Ti.sub.3.8 0 6.1 1.61-
1.60 0.612 Example 2
(Sm.sub.0.8Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.5T-
i.sub.5.8 0.2 6.1 1.61 1.60 0.607 Example 6
(Sm.sub.0.72Ce.sub.0.08Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.2-
5).sub.86.5Ti.sub.5.8 0.28 5.6 1.44 1.43 0.607 Example 7
(SM.sub.0.64Ce.sub.0.16Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.2-
5).sub.86.5Ti.sub.5.8 0.36 5 1.43 1.42 0.608 Comparative
(Sm.sub.0.48Ce.sub.0.32Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0-
.25).sub.86.5Ti.sub.5.8 0.52 4 1.42 1.41 0.608 Example 12
Comparative
(Sm.sub.0.4Ce.sub.0.4Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.2-
5).sub.86.5Ti.sub.5.8 0.6 3.5 1.42 1.41 0.609 Example 13
Comparative
(Sm.sub.0.32Ce.sub.0.48Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0-
.25).sub.86.5Ti.sub.5.8 0.68 3.1 1.41 1.40 0.609 Example 14
Comparative
(Sm.sub.0.16Ce.sub.0.64Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0-
.25).sub.86.5Ti.sub.5.8 0.84 2.3 1.39 1.38 0.610 Example 15 Example
8 (Sm.sub.0.72Nd.sub.0.08Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.2-
5).sub.86.5Ti.sub.5.8 0.28 5.6 1.45 1.44 0.607 Example 9
(Sm.sub.0.64Nd.sub.0.16Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.2-
5).sub.86.5Ti.sub.5.8 0.36 6 1.44 1.43 0.608 Comparative
(Sm.sub.0.48Nd.sub.0.32Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0-
.25).sub.86.5Ti.sub.5.8 0.52 3.9 1.5 1.49 0.608 Example 16
Comparative
(Sm.sub.0.4Nd.sub.0.4Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0.2-
5).sub.86.5Ti.sub.5.8 0.6 3.6 1.49 1.48 0.609 Example 17
Comparative
(Sm.sub.0.32Nd.sub.0.48Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0-
.25).sub.86.5Ti.sub.5.8 0.68 3.1 1.5 1.49 0.609 Example 18
Comparative
(Sm.sub.0.16Nd.sub.0.64Zr.sub.0.2).sub.7.7(Fe.sub.0.75Co.sub.0-
.25).sub.86.5Ti.sub.5.8 0.84 2.4 1.51 1.50 0.610 Example 19
In all samples, almost no .alpha.-(Fe, Co) phase was detected, and
the size and volume percentage of the phase were 1 .mu.m or less
and 3.5% or less, respectively. Along with addition of a rare earth
element having a negative Stevens factor, the anisotropic magnetic
field tends to be reduced. In the application to a magnet, when it
is used in a high-temperature environment of 100.degree. C. or
more, the Ha value is preferably 5 MA/m or more within which a high
coercive force can be expected. In the case of using the magnet in
the vicinity of room temperature, a large coercive force is not
required and therefore, it may also be possible to have an Ha value
of about 3 MA/m and configure a magnetic composition where the cost
and resource risk are reduced by adding surplus or low-cost Ce or
Zr to the raw material. Consequently, the fraction of R.sup.2 is
0.7 or less, more preferably 0.4 or less.
According to the present invention, in a compound having a
ThMn.sub.12-type crystal structure, represented by the following
formula:
(R.sup.1.sub.(1-x)R.sup.2.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.c-
M.sub.d, an element having a positive Stevens factor is used as the
rare earth element R.sup.1, so that uniaxial magnetic anisotropy
that is essential in a rare earth-based magnet can be imparted. In
addition, the cooling rate of molten alloy is adjusted in the
production process so as to decrease the amount of .alpha.-(Fe, Co)
phase precipitated at the time of cooling and precipitate many
ThMn.sub.12-type crystals, so that the anisotropic magnetic field
can be enhanced. Furthermore, the size specified in (2) above is
employed, and the size balance of respective hexagons is thereby
enhanced, so that a ThMn.sub.12-type crystal structure can be
stably formed. Moreover, the ratio of magnetic elements of Fe and
Co is increased by decreasing the T amount and in turn,
magnetization is improved.
* * * * *